Relationship between glycated hemoglobin and blood glucose levels in fasting and two hours after 75 g oral glucose in gestational diabetes mellitus

Abstract

Background: Oral glucose tolerance test (OGTT) performed at 24-28 weeks gestation is the current recommended method to the diagnosis of gestational diabetes mellitus (GDM). Many recent studies investigating glycated hemoglobin (HbA1c) in detecting GDM yield different results. There are no published data on HbA1c in the diagnosis of GDM in India. Methods: A cross-sectional study was carried out at T.N.M.C. Mumbai during the period from January to June 2021 to assess the reliability of HbA1c in the diagnosis of GDM. Results: We included 397 pregnant females. The age range of the patients was 18 to 35 years, with a mean of 24.57±11.10 years. The mean fasting blood glucose level was 129.73 mg/dl and the mean 2 hours after 75 g oral glucose level was 188.21 mg/dl. The difference between the two was statistically significant. The Spearman's correlation coefficient (r) between fasting blood glucose and HbA1c was 0.610 (p<0.05) and between postprandial blood glucose and HbA1c was 0.683 (p<0.05). Scatter plots of FBG and 2 hours after 75 g oral glucose with HbA1C shows a positive correlation. Conclusions: This study showed that 2 hours after 75 g oral glucose had a better correlation with HbA1c than fasting blood glucose level. In the absence of HbA1c facility or unreliable HbA1c report, postprandial blood glucose can be a surrogate marker of HbA1c for management and monitoring of gestational diabetes mellitus, but a larger study is needed to confirm this finding.